水文过程和生态过程的相互联系、相互影响是生态水文学研究的核心问题。水分是生态水文过程的主要驱动力，而干旱通过改变水分有效性直接影响生态水文过程进而导致流域生态系统组成、结构及功能发生改变，因此，在以变暖为主要特征的全球气候变化背景下，研究干旱条件下的生态水文过程变化对区域生态系统稳定具有重要意义。黄河是中华民族的母亲河，也是我国北方重要的生态屏障，而流经内蒙段的黄河流域属于生态环境脆弱区，生态系统逐渐退化，属于典型的干旱半干旱区。在气候变暖背景下，该区的生态水文过程发生改变，伴随着区域内干旱频率的增加，流域内生态水文过程受到进一步影响。因此，本论文主要以黄河流域内蒙段生态水文过程对干旱的响应为主题，首先对黄河流域内蒙段的干旱特征进行分析，从时间和空间两个维度来表征了流域内干旱的变化；此外，利用陆面过程模型对库布齐杨树林站的蒸散发（Evapotranspiration, ET）和植被总初级生产力（Gross primary productivity, GPP）进行了长序列时间的模拟，并得到了长时间序列的蒸腾比T/ET，进一步分析了干旱对ET和GPP及T/ET的影响；最后结合多种遥感数据，在空间上对ET和GPP对不同时间尺度干旱进行了响应分析，并结合植被类型数据，分析了不同植被类型下GPP、ET和水分利用效率（Water use efficiency, WUE）对干旱的响应，主要研究结果如下：

（1）对黄河流域内蒙古段的干旱时空变化特征进行分析发现，在时间上，流域在过去的60年呈显著的变干趋势，其气候在1992年发生了突变，在1992年之前以干旱湿润交替为主，但在1992-2012年期间，流域内干旱情况较为严重，在2013-2020年，流域整体干旱现象逐渐好转；流域内春季和夏季呈变干的趋势，秋季和冬季流域内有变湿趋势。在空间上，发现研究区内近40年的标准化降水蒸散发指数（Standardized precipitation evapotranspiration index, SPEI）在空间上变化不明显，西南部有向干旱转化的趋势，中部和东部的气候逐渐向湿润转化的变化趋势，且年际干旱频率高值区主要位于研究区南部和东部；在季节上，黄河流域内蒙古段春旱和夏旱较为严重，秋旱和冬旱的干旱频率相对较低。

（2）基于库布齐杨树林站应用了SiB2模型，获取了1980-2018年的生态水文要素数据，发现近40年GPP和ET值呈逐渐增加趋势。GPP与SPEI的变化趋势较一致，在较为干旱的年份，植被受到干旱胁迫或者发生死亡，导致GPP值下降。当流域内发生轻度或中度干旱时，ET与SPEI的变化较一致，ET随着干旱程度的增强而减少；当流域发生严重干旱或极端干旱且后一年降水增加的条件下，ET在干旱的后一年仍呈降低趋势，分析原因可能是由于干旱对植被的影响存在遗产效应，即流域内植被在遭受干旱后持续几年仍可能受到影响，导致植被蒸腾受到抑制。且流域在持续干旱条件下，随着干旱程度的变化T/ET基本保持不变，推测植被能根据外界环境进行自我调节并具备一定的抗干扰能力，且在长期持续干旱后，强降水能缓解土壤水分短缺，促使植被恢复正常生长。

         （3）通过实测数据对遥感产品进行验证，发现四类GPP（MODIS、AVHRR、PML_V2和GOSIF_GPP）和三类ET（MODIS、AVHRR和PML_V2）产品在该区域有较好的适用性。在生长季尺度上，四类GPP产品与四个时间尺度的SPEI值的时间变化曲线较为吻合，且1月、3月和6月时间尺度的SPEI比12月时间尺度的SPEI值更有优势；三类ET产品在生长季时间尺度上，各时间尺度下的SPEI值与ET的变化趋势较为一致，能反映出ET随SPEI值的响应情况。在夏季GPP与各时间尺度SPEI的相关性最高，冬季GPP与各时间尺度的SPEI的相关性最低，且GPP与SPEI_1、SPEI_3的相关性要优于SPEI_6和SPEI_12，表明GPP的变化对SPEI_1和SPEI_3的响应较为敏感，对干旱的响应较快；ET与各时间尺度下的SPEI的相关性在夏季和秋季要优于春季和冬季，ET与SPEI_1、SPEI_3的相关性要优于SPEI_6和SPEI_12。最后结合不同植被类型数据，发现在流域上森林区域的GPP和ET要大于灌木和草地，且对干旱响应敏感的是林地和灌木。在1982-2018年间，流域内四种植被类型的水分利用效率整体呈波动上升趋势，与干旱相关性较低，但是WUE与短时间尺度干旱的相关性要优于长时间尺度干旱。

The interconnection and interaction between hydrological and ecological processes are the core issues of ecohydrology research. Water is the main driver of ecohydrological processes, and drought directly affects ecohydrological processes by changing water effectiveness, which leads to changes in the composition, structure and function of watershed ecosystems. Therefore, in the context of global warming, it is important to study the changes of ecohydrological processes under arid conditions for regional ecosystem stability. The carbon and water cycles are key processes for ecosystems to maintain stability. Among which, Gross primary productivity(GPP) and  evapotranspiration(ET) of terrestrial ecosystems, as important components of the global carbon and water cycles, characterize the carbon sequestration and water consumption capacity of watersheds, and their changes visually reflect the extent to which ecohydrological processes are influenced by environmental changes. Therefore, gross primary productivity of vegetation and evapotranspiration were used as key elements of watershed ecohydrological processes to characterize the response of watershed ecohydrological processes in this study, and the response of watershed ecohydrological processes to drought was characterized by studying the response of total primary productivity of vegetation and evapotranspiration to drought.

The Yellow River is the mother river of the Chinese nation and an important ecological barrier in the north of China, while the Yellow River flowing through the section of Inner Mongolia belongs to the ecologically fragile zone with gradually degraded ecosystems and is an arid and semi-arid zone. In the context of climate warming, the ecohydrological processes in the region have changed. Along with the increase of drought frequency in the region, drought will have further influence on ecohydrological processes in the basin, and the study of ecohydrological processes under the influence of drought is of great significance to the overall regional regulation and optimal allocation of water resources. Therefore, this study focuses on the response of ecohydrological processes under drought in the Inner Mongolian section of the Yellow River basin. Firstly, the drought characteristics of the Inner Mongolian section of the Yellow River Basin were analyzed to characterize the trends of drought in the basin in both temporal and spatial dimensions.Then, the ET of evapotranspiration and GPP of vegetation at the site scale were temporally expanded using a land surface process model, and the results were used for drought response analysis to further analyze the changes of evapotranspiration distribution under drought. Finally, the response of ET and GPP to drought at different time scales was analyzed spatially by combining multiple remote sensing data, and the main findings were as follows:

(1) The temporal and spatial variation characteristics of drought in the Mongolian section of the Yellow River Basin were analyzed. It was found that in terms of time, the basin had a significant drying trend in the past 60 years, and the climate had a sudden change in 1992. Before 1992, the climate was mainly arid and humid, but during 1992-2012, the drought situation in the Basin was more serious. From 2013 to 2020, the overall drought phenomenon in the basin gradually improved. There was a dry trend in spring and summer, and a wet trend in autumn and winter. In the last 40 years, the SPEI values in the study area did not change significantly. The southwest part of the study area showed a trend of drought, while the central and eastern part of the study area showed a trend of humid. The regions with high annual drought frequency were mainly located in the southern and eastern part of the study area. In terms of season, spring and summer droughts are more serious in The Mongolian section of the Yellow River Basin, and the frequency of autumn and winter droughts is lower first.

(2) Affected by drought, the total primary productivity of vegetation will decrease, and so will evapotranspiration. After drought occurred in the second year, the drought relief, evaporation will be significantly lower, analysis the reason is that by the second annual rainfall increased soil water deficit, one year before increase caused by soil evaporation, further analyzes the transpiration than T/ET response to drought, found in the case of continuous drought, T/ET and the ET range are smaller, The results showed that vegetation could adjust itself according to the external environment under drought condition, which played a certain role in maintaining the stability of ecosystem.

(3) It is found that four types of GPP and three types of ET products have good applicability in this region by verifying remote sensing products with measured data. At the growth season scale, the SPEI values of the four types of GPP products were consistent with those of the four time scales, and the SPEI values of January, March and June were more advantageous than those of December. In the time scale of growth season, the SPEI values of the three types of ET products were consistent with the change trend of ET at each time scale, which could reflect the response of ET with SPEI values. The correlation between GPP and SPEI was the highest in summer and the lowest in winter, and the correlation between GPP and SPEI_1 and SPEI_3 was better than that of SPEI_6 and SPEI_12, indicating that GPP was sensitive to SPEI_1 and SPEI_3. Faster response to drought; The correlation between ET and SPEI at different time scales was better in summer and autumn than in spring and winter, and the correlation between ET and SPEI_1 and SPEI_3 was better than SPEI_6 and SPEI_12. Finally, combined with the data of different vegetation types, it was found that the GPP and ET of forest area were larger than those of shrub and grassland.